docs(chart): document extraVolumes and extraVolumeMounts in the Helm install guide

The install guide lists extraEnv and extraEnvFrom but had no word on the
new volume values. Add a Further volumes section with the KItinerary
extractor example and point the Reservations-and-Bookings page at it.

charts/README.md

@@ -5,7 +5,7 @@ This is a minimal Helm chart for deploying the TREK app.
 ## Features
 - Deploys the TREK container
 - Exposes port 3000 via Service
-- Optional persistent storage for `/app/data` and `/app/uploads` and extra volumes support
+- Optional persistent storage for `/app/data` and `/app/uploads`, plus extra volumes and mounts
 - Configurable environment variables and secrets
 - Optional generic Ingress support
 - Configurable health checks (liveness/readiness probes) on `/api/health`

wiki/Install-Helm.md

@@ -231,6 +231,21 @@ extraEnvFrom:
       name: trek-smtp
 ```
 
+### Further volumes
+
+`extraVolumes` adds volumes to the pod, and `extraVolumeMounts` mounts them in the TREK container, next to `/app/data` and `/app/uploads`. Both go into the Deployment as written, and the chart does not create the objects they name. For example, to give the booking import your own KItinerary extractors from a ConfigMap (one `.json` and one `.js` key for each extractor, see [Reservations-and-Bookings](Reservations-and-Bookings#your-own-extractors)):
+
+```yaml
+extraVolumes:
+  - name: kitinerary-extractors
+    configMap:
+      name: trek-kitinerary-extractors
+extraVolumeMounts:
+  - name: kitinerary-extractors
+    mountPath: /usr/local/share/kitinerary/extractors
+    readOnly: true
+```
+
 ### Ingress
 
 ```yaml

wiki/Reservations-and-Bookings.md

@@ -216,7 +216,7 @@ services:
       - ./extractors:/usr/local/share/kitinerary/extractors:ro
 ```
 
-With the Helm chart, mount a ConfigMap there with `extraVolumes` and `extraVolumeMounts`. See the example in the chart's `values.yaml`.
+With the Helm chart, mount a ConfigMap there with `extraVolumes` and `extraVolumeMounts`. See [Install-Helm](Install-Helm#further-volumes).
 
 ### Review mark